Submicron tin oxide (SnO2) was obtained from thermal decomposition of tin oxalate (SnC2O4) precipitated at room temperature from amixture of solutions of tin (II) chloride (SnCl2) and oxalic acid (H2C2O4). Aqueous precipitation of SnC2O4 was firstly investigated by parametersvariation of starting material concentrations, addition methods and mixing times. Upon calcination, SnO2 powder tacky and subsequent grinding was found to cause nanosized SnO2 particles to agglomerate into plates. Aqueous??alcohol precipitation was then developed, based on the previously conducted aqueous precipitation Stabilisation of SnO2 suspensions was found to be better in aqueous rather than non??aqueous media, as determined by zeta potential analysis and sedimentation tests. A detailed concept of the effects of zeta potential and sedimentation (enhanced sedimentation region (ESR)) on colloidal processing, i.e., suspension stability, was introduced. Two systems, Sn??Al??O and Sn??Si??O, were investigated at their invariant temperatures and ternary phase diagrams, which haven??t been reported elsewhere, were constructed (at nine isothermal temperatures each). The binary diagram for the system SnO2??SiO2, which has not been reported in the literature, was constructed. The systems compatibilities were confirmed experimentally at 1000oC, with incidental finding of micron??sized fibres of single crystal SnO2 with preferential [110] growth direction obtained. It was also deduced that 1000oC can be used for SnO2 coatings sintering without undesired reaction or mutual solubility. Successful electrophoretic deposition (EPD) of commercial SnO2 powder on dense sapphire was obtained by the use of pH 2 SnO2 suspension, but not with pH 9 suspensions leading to a review of the basis for EPD requirements in terms of suspension properties. Thus, another conceptual approach to EPD processing and setup was proposed in terms of zeta potential, suspension stability and net particle charge. Obtained homogeneous deposition of commercial SnO2 powders contradicted the findings of published works of EPD on insulating dense substrates. Thus critical factors in the design of EPD processing on dense insulating substrates and associated mechanisms responsible for the deposition were developed. However, EPD of synthesised SnO2 powders yielded inhomogeneous coatings, even with voltage application of up to 30 V. Microcell effects, which were deduced based on localised particle leaching in the suspension, were proposed. Although deposition was relatively unsuccessful, this demonstrated possibility of aqueous EPD with the usage of high voltages without occurrence of water electrolysis which hasn??t been observed in literature.
| Identifer | oai:union.ndltd.org:ADTP/272570 |
| Date | January 2009 |
| Creators | Taib, Hariati, Materials Science & Engineering, Faculty of Science, UNSW |
| Publisher | Awarded By:University of New South Wales. Materials Science & Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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